Clarify that all platforms we support have a C platform

Author: gnzlbg

reference/src/layout/scalars.md

@@ -38,10 +38,9 @@ They have the same layout as the [pointer types] for which the pointee is
 `Sized`, and are layout compatible with C's `uintptr_t` and `intptr_t` types.
 
 > **Note**: C99 [7.18.2.4](https://port70.net/~nsz/c/c99/n1256.html#7.18.2.4)
-> requires `uintptr_t` and `intptr_t` to be at least 16-bit wide. That is, on
-> all platforms that we currently support, which have a C platform,
-> `isize`/`usize` are at least 16-bit wide. Currently, `libcore` unconditionally
-> provides impls of `From<i16>`/`From<u16>` for `isize`/`usize`.
+> requires `uintptr_t` and `intptr_t` to be at least 16-bit wide. All 
+> platforms we currently support have a C platform, and as a consequence,
+> `isize`/`usize` are at least 16-bit wide for all of them.
 
 > **Note**: Rust's `usize` and C's `unsigned` types are **not** equivalent. C's
 > `unsigned` is at least as large as a short, allowed to have padding bits, etc.